22 GEOLOGY OF THE COMSTOCK LODE. 



side of the fissure on the other, at the time of the formation of the vein, 

 caused protuberances of one wall to meet such of the other, and concave 

 places to come opposite to each other. This is the reason why every large 

 fissure vein is liable to repeated expansions and contractions, though the 

 former prevail largely over the latter. It is to be expected that the Com- 

 STOCK Lode will exhibit the same feature in its downward course to indefi- 

 nite depth, as it has done heretofore, though its general width will probably 

 remain nearly equal to that which it possesses in the lowest works. The 

 formation of large horses is, from the nature of their origin, more peculiar 

 to upper than to lower levels, since their breaking down from the hanging 

 wall will in every fissure be most apt to take place where the latter is of 

 comparatively inferior thickness, than where it is hundreds or thousands of 

 feet wide. But small fragments may separate from it at any depth, and 

 their quantity will chiefly depend upon the nature of the rock and the power 

 of decomposing agents. If any change as to the inclosing rocks should 

 occur in depth, it is probable that propylite will disappear on the western 

 side and syenite predominate there more and more. 



Probable character of the Lode in depth. All thc CvidcnCCS iu the UppCr IcVcls 



justify the expectation that the foot wall will continue with its smooth and 

 regular clay-selvage, while the irregularity and indistinctness of the eastern 

 side will not diminish but rather increase as its true character as hanging 

 wall will become more conspicuous. The vertical sheets of clay which 

 have from time to time been cut in the adits east of the vein, rise undoubt- 

 edly from the hanging wall. Clay seams within the body of the vein will 

 probably diminish with the increase of unity in inclination. Those which 

 are at present observable at upper levels are particular!}' occasioned by 

 the vertical position of the vein-matter, which of course facilitates sliding 

 motions. Larger accumulations of clay will especially continue near the 

 old ravines. 



The ores, througli all the levels explored, retain the character of true 

 silver ores which they had near the surface. The amount of lead, copper, 

 iron, and zinc has never been large in the Comstock ores, and these metals 

 preserve now at the lowest levels nearly the same relative proportion as 

 formerly. Their increase, especially of lead, would be the most unfavora- 



